Ultrasound technology has been used for therapeutic and diagnostic medical procedures, which can include providing imaging of internal portions of a body. For example, devices have been proposed for using ultrasound imaging within blood vessels to view the condition of the vessel and/or placement or condition of a device placed in the vessel. However, a number of problems with such devices remain. For example, many such devices provide at best an image of a cross section of tissue or other items of interest, i.e. a thin, disk-shaped slice of the interior of a blood vessel with a portion in the center that is not within the range of the ultrasound beam. In some other devices, the ultrasound beam is directed at a fixed angle that is not substantially perpendicular to the longitudinal axis (e.g. at 45 degrees). In this case the imaged region is static in the form of a portion of the surface of a cone, also with a center portion that is not within the range of the ultrasound beam. In either case, in order to visualize the entirety of a significant length within the body (e.g. surfaces or portions of tissue, or of devices), the device must be moved along that length, with respective images of cross sections at particular locations taken. Such movement may be inexact, and may include risks associated with blind insertion of the device through the vessel. It is also slow. Typical pull back images take on the order of 30 s to perform (at a speed of about 0.1 mm/s). Additionally, any changes in the orientation of the transducer during pullback distort the image.
Three-dimensional information provides the added value that it can be used to help in navigation of devices within the vasculature and confirmation of position of the devices. In an intravascular example, catheters can be moved up and down vessels and the image data obtained via ultrasound can be combined or otherwise processed in order to create three-dimensional information. However, the catheter tip motion and angle must be known in order to produce accurate and usable data. Three-dimensional images may be acquired by one-dimensional arrays connected to a mechanical actuator, to move the arrays within the catheter or other device. Such designs are expensive and generally require more space in a device than many vessels will permit. To achieve good image quality, such array transducers must simultaneously transmit and receive on many separate channels. That condition requires several expensive and bulky coaxial cables. Fewer coaxial cables can be used, but doing so reduces the quality of the image and image frame rate.
Ultrasound devices have been proposed which include a motion of a transducer about two axes to provide three-dimensional information. However, the mechanical mechanisms that provide such movement tend to be bulky and require dimensions which are unsuitable for applications in small body areas. Additionally, the problem of providing motion to a transducer must be solved. Designs including torque cables can be problematic. Practically, a sufficiently maneuverable torque cable creates a potential for delay in the transferring of torque from one end of the cable to the other, as the cable stores and releases elastic energy, which causes the transducer assembly to rotate at a non-uniform rate even when the rotation source rotates at a uniform rate. The non-uniform rotation rate causes the resulting data or images to be distorted. These problems are magnified if two torque cables are used for two-axis movement of the transducer. In some cases, separate motors can be used to provide movement to the transducer. However, motors require additional space and can include further disadvantages such as control wires or structural components which cross the viewing window and cause a portion of an image to be blocked. Additionally, existing feedback mechanisms for controlling complex motor motion can be costly and bulky.
There remains a need for accurate and efficient application of ultrasound in three dimensions along a substantial length of a small body area, for example to provide a physician with a real-time view along that length. There also remains a need for devices that can view a medical device and one or more tissues or tissue parts simultaneously, particularly in cases in which the device and tissue(s) could not have been imaged reliably in any two-dimensional plane.